Merge pull request #187 from acevest/master

fix typo

eBook/10.7.md

@@ -51,7 +51,7 @@ func (tn *TwoInts) String() string {
 type TT float64
 
 func (t TT) String() string {
-    return fmt.Sprintf("%v", s)
+    return fmt.Sprintf("%v", t)
 }
 t. String()
 ```